A major fix to the way in which a select() object produces

labeled columns when apply_labels() is used; this mode
produces a SELECT where each column is labeled as in
<tablename>_<columnname>, to remove column name collisions
for a multiple table select.   The fix is that if two labels
collide when combined with the table name, i.e.
"foo.bar_id" and "foo_bar.id", anonymous aliasing will be
applied to one of the dupes.  This allows the ORM to handle
both columns independently; previously, 0.7
would in some cases silently emit a second SELECT for the
column that was "duped", and in 0.8 an ambiguous column error
would be emitted.   The "keys" applied to the .c. collection
of the select() will also be deduped, so that the "column
being replaced" warning will no longer emit for any select()
that specifies use_labels, though the dupe key will be given
an anonymous label which isn't generally user-friendly.
[ticket:2702]

2 files changed, 58 insertions, 22 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 5a3a92a3e..b902f9ffc 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -992,13 +992,15 @@ class SQLCompiler(engine.Compiled):
         else:
             self.result_map[keyname] = name, objects, type_
 
-    def _label_select_column(self, select, column, populate_result_map,
+    def _label_select_column(self, select, column,
+                                    populate_result_map,
                                     asfrom, column_clause_args,
+                                    name=None,
                                     within_columns_clause=True):
         """produce labeled columns present in a select()."""
 
         if column.type._has_column_expression and \
-            populate_result_map:
+                populate_result_map:
             col_expr = column.type.column_expression(column)
             add_to_result_map = lambda keyname, name, objects, type_: \
                                 self._add_to_result_map(
@@ -1023,13 +1025,11 @@ class SQLCompiler(engine.Compiled):
             else:
                 result_expr = col_expr
 
-        elif select is not None and \
-                select.use_labels and \
-                column._label:
+        elif select is not None and name:
             result_expr = _CompileLabel(
                     col_expr,
-                    column._label,
-                    alt_names=(column._key_label, )
+                    name,
+                    alt_names=(column._key_label,)
                 )
 
         elif \
@@ -1037,7 +1037,7 @@ class SQLCompiler(engine.Compiled):
             isinstance(column, sql.ColumnClause) and \
             not column.is_literal and \
             column.table is not None and \
-            not isinstance(column.table, sql.Select):
+                not isinstance(column.table, sql.Select):
             result_expr = _CompileLabel(col_expr,
                                     sql._as_truncated(column.name),
                                     alt_names=(column.key,))
@@ -1098,11 +1098,11 @@ class SQLCompiler(engine.Compiled):
         # correlate_froms.union(existingfroms)
 
         populate_result_map = force_result_map or (
-                                compound_index == 0 and (
-                                    not entry or \
-                                    entry.get('iswrapper', False)
-                                )
-                            )
+                                        compound_index == 0 and (
+                                            not entry or \
+                                            entry.get('iswrapper', False)
+                                        )
+                                    )
 
         self.stack.append({'from': correlate_froms,
                             'iswrapper': iswrapper})
@@ -1117,10 +1117,12 @@ class SQLCompiler(engine.Compiled):
         # the actual list of columns to print in the SELECT column list.
         inner_columns = [
             c for c in [
-                self._label_select_column(select, column,
+                self._label_select_column(select,
+                                    column,
                                     populate_result_map, asfrom,
-                                    column_clause_args)
-                for column in util.unique_list(select.inner_columns)
+                                    column_clause_args,
+                                    name=name)
+                for name, column in select._columns_plus_names
                 ]
             if c is not None
         ]
diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index 5cef778bb..28b1c6ddd 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -5781,13 +5781,47 @@ class Select(HasPrefixes, SelectBase):
         fromclause = _interpret_as_from(fromclause)
         self._from_obj = self._from_obj.union([fromclause])
 
+
+    @_memoized_property
+    def _columns_plus_names(self):
+        if self.use_labels:
+            names = set()
+            def name_for_col(c):
+                if c._label is None:
+                    return (None, c)
+                name = c._label
+                if name in names:
+                    name = c.anon_label
+                else:
+                    names.add(name)
+                return name, c
+
+            return [
+                name_for_col(c)
+                for c in util.unique_list(_select_iterables(self._raw_columns))
+            ]
+        else:
+            return [
+                (None, c)
+                for c in util.unique_list(_select_iterables(self._raw_columns))
+            ]
+
     def _populate_column_collection(self):
-        for c in self.inner_columns:
-            if hasattr(c, '_make_proxy'):
-                c._make_proxy(self,
-                        name=c._label if self.use_labels else None,
-                        key=c._key_label if self.use_labels else None,
-                        name_is_truncatable=True)
+        for name, c in self._columns_plus_names:
+            if not hasattr(c, '_make_proxy'):
+                continue
+            if name is None:
+                key = None
+            elif self.use_labels:
+                key = c._key_label
+                if key is not None and key in self.c:
+                    key = c.anon_label
+            else:
+                key = None
+
+            c._make_proxy(self, key=key,
+                    name=name,
+                    name_is_truncatable=True)
 
     def _refresh_for_new_column(self, column):
         for fromclause in self._froms: